platform:x86: add Intel P-Unit mailbox IPC driver

This driver provides support for P-Unit mailbox IPC on Intel platforms.
The heart of the P-Unit is the Foxton microcontroller and its firmware,
which provide mailbox interface for power management usage.

Signed-off-by: Qipeng Zha <qipeng.zha@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>
diff --git a/drivers/platform/x86/Makefile b/drivers/platform/x86/Makefile
index 3ca78a3..5ee5425 100644
--- a/drivers/platform/x86/Makefile
+++ b/drivers/platform/x86/Makefile
@@ -62,3 +62,4 @@
 obj-$(CONFIG_ALIENWARE_WMI)	+= alienware-wmi.o
 obj-$(CONFIG_INTEL_PMC_IPC)	+= intel_pmc_ipc.o
 obj-$(CONFIG_SURFACE_PRO3_BUTTON)	+= surfacepro3_button.o
+obj-$(CONFIG_INTEL_PUNIT_IPC)  += intel_punit_ipc.o